Infrared concentrating emitter

ABSTRACT

A metallic plate coated on one side with plasma sprayed stainless steel is mounted transversely within a cylindrical housing. Metallic cylinders having different lengths are concentrically disposed within the housing and extend from coated side of plate. Plate is electrically heated, causing coating thereon to radiate infrared rays which are filtered by a polyimide sheet extended across end of housing.

United States Wellnitz et a1.

1 Nov. 7, 1972 INFRARED CONCENTRATING EMITTER Inventors: Jerry N. Wellnitz, La Mesa; Richard S. Dummer, Escondido, both of Calif.

Assignee: Rohr Industries, Inc.

Filed: Oct. 24, 1969 Appl. No.: 869,263

US. Cl. ..2l9/553, 219/345, 219/347, 219/354, 250/88, 350/1 Int. Cl. ..H05b 3/10 Field of Search ..2l9/345, 347, 349, 354, 553; 250/88, 89; 350/1 References Cited UNITED STATES PATENTS 2/1970 Wells ..219/354 X 3/1951 Callender ..2l9/345 Primary Examiner-R. F. Staubly Att0mey-George E. Pearson [5 7] ABSTRACT A metallic plate coated on one side with plasma sprayed stainless steel is mounted transversely within a cylindrical housing. Metallic cylinders having different lengths are concentrically disposed within the housing and extend from coated side of plate. Plate is electri-,

cally heated, causing coating thereon to radiate 1 1];

frared ys ghich are filtered by a polyimide sheet exmed cross end of housing.

8 Claims, 2 Drawing Figures INFRARED CONCENTRATING EMITTER SUMMARY OF THE INVENTION This invention relates to infrared radiation apparatus and more particularly to such apparatus which can simulate the heat radiation characteristics of aircraft jet engines and rockets.

The effectiveness of heat-sensitive tracking devices used in ground-to-air and air-to-air missiles can be determined by tests conducted with target drones carrying apparatus capable of emitting infrared radiation with the wavelength pattern which said devices are designed to seek. The invention disclosed herein provides such infrared emitting apparatus which can readily be adapted to produce infrared radiation in a variation of wavelength patterns which closely match the infrared rays radiated by different aircraft jet engines and rockets. In addition, infrared radiation apparatus in accordance with the invention is light in weight and relatively inexpensive, which makes it particularly advantageous for use in target drones.

A preferred embodiment of the disclosed invention comprises a cylindrical housing formed of metal and covered at one end thereof by a thin sheet of polyimide. Transversely disposed within the housing and electrically connected therewith is a disk-shaped copper plate having electric heating elements embedded in grooves formed in the side thereof remote from the polyimide sheet. The other side of the copper plate is coated with a thin layer of an alloy containing iron and chromium, said layer being deposited on the'plate by spraying particles of the alloy thereon in plasma form. A plurality of metallic pins project from the alloy-coated side of the plate and are respectively spaced apart on concentric circles thereon. Mounted on the free ends of the pins (i.e., the ends of said pins not attached to the plate) and thus disposed in concentric relation with the housing are a plurality of thin-walled, metallic cylinders which are graduated in length. Preferably the cylinders are formed of an alloy of iron and chromium and are electroplated with nickel silver and then with gold. A partition formed of a heat-resistant and electrical-insulative material extends transversely across the interior of the housing in spaced relation with the side of the plate which has the electric heating elements attached thereto, and electric conduits connect the latter to an electric power supply and are sheathed in tubes which pass through apertures in said partition, said tubes also being formed of a heat-resistant and electrical-insulative material. The space between the plate and the partition is filled with thermal insulation such as asbestos, and one end of each electric heating element is also electrically connected to the plate, which in turn is electrically connected with the power supply through the metallic housing.

When the plate is heated by the flow of electric current through the heater elements, radiant energy in the infrared spectrum is radiated from the alloy-coated side thereof. The cylinders concentrate this energy into a beam having the desired geometric configuration, and the polyimide sheet at the end of the housing filters said beam so that it has the required wavelength range for simulation of a heat source such as a jet engine.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of the preferred embodiment of the invention; and

FIG. 2 is a longitudinal section of the same embodiment, taken along the plane represented by line 22 in FIG. 1 and in the direction indicated by arrows therein.

DETAILED DESCRIPTION In the drawings reference number 10 designates generally a cylindrical housing comprising a forward section 12 and an aft section 14 which are secured to each other in coaxial, end-to-end relation by means of an inner ring 16 attached to the inner surface of the aft section and projecting within the adjoining end of the forward section, a spacing ring 18 disposed between said inner ring and said forward section, and screws 20 which pass through holes in said forward section, spacing ring, and inner ring and which are engaged with nuts 22 so as to clamp the last-named components together. Preferably the forward and aft sections of the housing and their connecting components are formed of a corrosion-resistant metal such as a stainless steel.

Fixedly mounted in circumferentially spaced relation adjacent the inner surface of forward section 12 of the housing and located intermediate the ends thereof are a plurality of L-shaped brackets 24. More specifically, each bracket is mounted on the forward section 12 by means of a screw 26 which passes through a hole in the latter, through a washer 28 which is disposed between the bracket and the wall of said forward section, and through a hold in one leg of said bracket, a nut 30 being engaged with the end of said screw to clamp the lastnamed components together. The brackets 24, screws 26, and nuts 30 are also preferably formed of a stainless steel, whereas washer 28 is preferably formed of a heatresistant material such as asbestos or a ceramic. The inwardly projecting legs of brackets 24 extend over the edge of a circular plate 32 and are fastened thereto by means of screws 34 which respectively pass through holes in said legs and which are threadedly engaged within holes in said plate, thus holding the latter in fixed position within housing 10 transversely to the longitudinal axis thereof. Plate 32 is preferably formed of copper or an alloy thereof, and the surface thereof which is uppermost in FIG. 2 is coated with a stainless steel by a technique which will be described hereinafter. The other side of the platehas a series of interconnected, circumferentially extending grooves formed therein, and electric heating elements 36 are positioned in these grooves. More particularly, each heating element comprises an electric conductor one end of which is grounded to plate 32 and the other end of which is connected to the terminal strip 38 of a respective one of three leads 40a 40c, a sheath of electrical-insulative material which surrounds said conduit, and a metallic sheath which surrounds said insulative material and is welded to said plate. Leads 40a 40c extend through holes in a partition 42 which is formed of a heat-resistant, electrical-insulative material such as fiber glass and the edge of which rests upon inner ring 16 and spacing ring 18. Between plate 32 and partition 42 the interior of housing 10 is filled with a thermal-insulative material 44, such as Kaowool. The ends of the conductors of leads 40a 400 which are lowermost in FIG. 2 are secured to a bus bar 46 by nuts 48a, 48b engaged therewith, and the terminal 50 of an electric conduit 52 is clamped between the nuts on one of the leads.

A plurality of pins 54 is respectively disposed within holes in plate 32 and project from opposite sides of the latter, which holes are respectively spaced apart on three circles concentrically disposed relatively to housing 10. The portion of each pin which projects from the coated side of the plate has a slot extending axially thereof, and the portion of the pin which projects from the other side of said plate is threaded. Three cylindrical tubes 56a 56c are disposed in concentric, spaced relation within the housing, their lower edges being respectively engaged within the slots in the pins 54 located on a respective one of the aforesaid circles and abutting washers 58 which are positioned on said pins and which rest upon the coated side of plate 32. Preferably the tubes are welded to the pins, and a pair of nuts 60a, 60b engage the threaded ends of each of the latter to hold the tubes in proper position. The tubes are made of a stainless steel such as that identified as SAE 30321, and their inner surfaces (i.e., the surfaces remote from housing are preferably electroplated with nickel silver and then with gold to make the same good reflectors of infrared energy. It will also be noted that the tubes are graduated in length as well as diameter, the outer tube 56a being longer than the middle tube 56b and the latter being longer than the inner tube 56c.

At the end of housing 10 which is adjacent tubes 56a 56c there are a plurality of circumferentially spaced, countersunk holes. Flat-head screws 62 are respectively disposed within these holes and project through washers 64 which abut the inner surface of said housing, holes in a ring 66 which abuts said washers, holes in another ring 68 which is disposed inside ring 66, and holes in a diathermic sheet 70 the edge portion of which is held between said rings and the remainder of which extends transversely across the end of said housing, nuts 72 being respectively engaged with said screws to retain the aforesaid components in the described and illustrated position. Screws 62, nuts 72, and rings 66, 68 are preferably formed of a corrosionresistant metal such as a stainless steel. In the specific embodiment of the invention which is being described, sheet 70 is formed of polyimide sold by Du Pont Corporation under the designation Kapton Type h, and the thickness of the sheet is 0.001 inch.

As mentioned hereinbefore, the surface of plate 32 adjacent tubes 56a 56c is coated with a stainless steel, preferably SAE30321. This metal is deposited on the plate by spraying the same thereon in the form of ionized particles. Preferably the plasma spray equipment manufactured by Plasmadyne Corporation is utilized for this purpose, and a coating of stainless steel having a thickness of about 0.005 to 0.010 inch is applied to the plate.

Although the apparatus is not limited to a particular size, in the embodiment which is described and illustrated the inside diameter of housing 10 is about 8.0 inches, the distance between sheet 70 and plate 32 is about 3.75 inches, and the thickness of said plate is about 0.25 inches.

OPERATION The end of housing 10 which is cut away in FIG. 2 is generally attached by suitable means to a target drone so that the longitudinal axis of said housing is substantially parallel with the longitudinal axis of the drone. Conduit 52 is connected with an electric power supply carried by the target drone, and during the operation of the described apparatus electric current flows through said conduit to bus bar 46, then through leads 40a 40c, heating elements 36, plate 32, brackets 24, screws 26, housing 10, and a conduit (not shown) which is connected with said housing and power supply. The design of the apparatus is such that with an input of 1,300 watts to heating elements 36 the temperature of plate 32 is approximately 1,400 F. when the apparatus is operating at sea level. Infrared energy having statistical distribution in all wavelengths is thus emitted from the coating of stainless steel on plate 32, and this energy is concentrated by tubes 56a 560 to form a beam the longitudinal axis of which is coincident with the longitudinal axis of housing 10. The polyimide sheet passes infrared energy in the wavelength range of 1 to 6 microns.

When tubes 56a 560 are arranged as illustrated in the drawings, the infrared beam which passes through sheet 70 closely simulates the infrared radiation pattern produced by a particular type of jet engine which is used to propel military aircraft. The infrared emission characteristics of other types of jet engines, rocket motors and the like can readily be simulated by varying the arrangement of said tubes. For example, the length-todiameter ratio of the tubes can be varied to change the divergence of the infrared beam which passes through sheet 70. In some instances the innermost tubes may advantageously be longer than the outer tube.

It has been found that the coating of SAE30321 stainless steel, applied to plate 32 in the form of plasma as aforesaid, is an excellent emitter of infrared energy for the purpose of simulation of high-temperature heat sources such as jet engines. However, other emissive coatings (including other stainless steels applied in plasma form) may also be employed in apparatus in accordance with the invention. Polyimide has also been found very effective as a filtering material for use in apparatus constructed in accordance with the principles of the invention and used to simulate the infrared radiation of an aircraft jet engine. In addition, the polyimide filter is inexpensive. Persons skilled in the art of infrared radiation apparatus will recognize, however, that other materials may be substituted for the polyimide used in the preferred embodiment of the invention. Hence, it will be understood that various modifications can be made in the apparatus which has been disclosed, without departing from the scope of the invention as defined in the appended claims.

What is claimed as new and useful and desired to be secured by U. S. Letters Patent is:

1. Infrared apparatus comprising:

a tubular housing;

a heat-conductive plate mounted within said housing transverse to the longitudinal axis thereof;

a coating on one side of said plate capable of emitting heat radiation efficiently in a predetermined wave length range;

a plurality of heat-reflective tubes one end of each of which is located closely adjacent the coated side of said plate, said tubes being arranged in nested, spaced relation with the length of said tubes increasing as the distance between said tubes and the longitudinal axis of said housing increases;

a sheet disposed across the end of said housing on the coated side of said plate and formed of amaterial capable of transmitting heat radiation in a predetermined wavelength range; and

means operatively associated with said apparatus for heating the side of said plate remote from said coating.

2. Apparatus as defined in claim 1 wherein said coating is deposited on said plate by spraying the same thereon in the form of plasma.

3. Apparatus as defined in claim 1 wherein said housing and tubes are cylindrical and concentrically disposed relative to one another.

4. Apparatus as defined in claim 1 wherein said sheet is formed of polyimide.

5. Apparatus as defined in claim 1 wherein said tubes are formed of an alloy containing principally iron and chromium.

6. Apparatus as defined in claim 1 wherein said material coated on said plate is an alloy containing principally iron and chromium.

7. Apparatus as defined in claim 1 wherein said means for heating the side of said plate remote from said coating comprises electric heating elements disposed against said side.

8. infrared apparatus comprising:

a cylindrical housing;

a metallic plate mounted within said housing transverse to the longitudinal axis thereof;

a coating on one side of said plate consisting of an alloy containing principally iron and chromium and deposited on said plate by plasma spraying;

a plurality of cylindrical tubes one end of each of which is located closely adjacent the coated side of said plate, said tubes being formed of an alloy containing iron and chromium and being disposed in concentric, spaced relation relative to said housing with the length of said tubes increasing as the distance between said tubes and the longitudinal axis of said housing increases;

a sheet of polyimide disposed across the end of said housing on the coated side of said plate; and

a plurality of electric heating elements disposed against the side of said plates remote from said coating. 

2. Apparatus as defined in claim 1 wherein said coating is deposited on said plate by spraying the same thereon in the form of plasma.
 3. Apparatus as defined in claim 1 wherein said housing and tubes are cylindrical and concentrically disposed relative to one another.
 4. Apparatus as defined in claim 1 wherein said sheet is formed of polyimide.
 5. Apparatus as defined in claim 1 wherein said tubes are formed of an alloy containing principally iron and chromium.
 6. Apparatus as defined in claim 1 wherein said material coated on said plate is an alloy containing principally iron and chromium.
 7. Apparatus as defined in claim 1 wherein said means for heating the side of said plate remote from said coating comprises electric heating elements disposed against said side.
 8. Infrared apparatus comprising: a cylindrical housing; a metallic plAte mounted within said housing transverse to the longitudinal axis thereof; a coating on one side of said plate consisting of an alloy containing principally iron and chromium and deposited on said plate by plasma spraying; a plurality of cylindrical tubes one end of each of which is located closely adjacent the coated side of said plate, said tubes being formed of an alloy containing iron and chromium and being disposed in concentric, spaced relation relative to said housing with the length of said tubes increasing as the distance between said tubes and the longitudinal axis of said housing increases; a sheet of polyimide disposed across the end of said housing on the coated side of said plate; and a plurality of electric heating elements disposed against the side of said plates remote from said coating. 